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Hydrophone Drawing Way Too Much Current

  1. Jan 23, 2012 #1
    I have an underwater microphone "hydrophone" that should run on 12vDC and 45mA. Except that when I run it off of my power supply, it is wanting to draw around 3Amps of current at the 12volts. The three power wires are (+, -, and shield) and are correspondingly connected to the power supply's terminals (+, -, ground). This maybe the most retarded question ever but should I be getting continuity between the (+ and -) wires of the power cable? The differential output is wired to an XLR connector going into a data acquisition system. I don't know why this is drawing so much amperage!? What could be causing this? Are there any short circuiting tests or grounding issues that I should look for? Thank you so much.
     
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  3. Jan 23, 2012 #2

    DaveC426913

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    Does it draw the same current when out of the water? :smile:
     
  4. Jan 23, 2012 #3
    Yes, it does not matter if it is out of water or in the water, it behaves the same way
     
  5. Jan 23, 2012 #4

    Bobbywhy

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    If the hydrophone specification states "12V @ 45mA" and it draws 3 Amps!! NO, you should not get continuity between them. Do you mean zero ohms?
    Using Ohm's Law dividing 12 volts by 45 mA results is around 266 Ohms. This is the expected DC resistance of the load in the hydropone. It sounds like there is a short circuit somewhere between plus and minus wires or the plus and shield.
    You need to find the short. Look in the most likely places first-connectors, damage to the cable's outer jacket allowing water in, or a blown component in the hydrophone itself.
     
  6. Jan 24, 2012 #5
    Is the hydrophone a piezoelectric transducer?? Are you applying DC power supply directly to the transducer, and bypassing the driver?
     
  7. Jan 24, 2012 #6
    Be very careful applying out of water, you can damage a hydrophone that way
     
  8. Jan 25, 2012 #7

    Bobbywhy

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    Will you please explain why you think the hydrophone would be damaged if the normal operating power was applied when out of the water? A hydrophone can operate in water or air without damage.

    It is true that for sonar transducers that transmit lots of power, also known as "projectors" will probably be damaged if transmitting power pulses are applied in air. This is because of the tremendous acoustic impedances difference between the water and the air. The piezoelectric element(s) can literally vibrate so intensley that they fracture.
     
    Last edited: Jan 25, 2012
  9. Jan 25, 2012 #8
    You answered your own question. They can fracture AND overheat.
     
  10. Jan 25, 2012 #9

    Bobbywhy

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    Hydrophones do not transmit high intensity acoustic power as in a transmitting projector.

    Hydrophones receive and detect acoustic energy (like a sonar echo) that is extremely low in power. They CAN receive and detect sound energy in air without damage like fracturing and overheating.
     
  11. Jan 26, 2012 #10
    I suppose you're right about your definitions, my Urick book defines a projector as the transmitter and a hydrophone as the receiver. But if we stick to that definition, then a hydrophone should not be transmitting. If we loosen the definition, and just call it a transducer, then it can do both, and that is what the OP is doing.

    However, I see no definition that a hydrophone is for low power applications and projectors are for high power applications. This is specific to the transducer and its design, not what its name is.

    You say they can receive and detect energy in air, which is true. But if you drive it with power in air, you need to be cautious to not damage it because they are designed to work in water and it is very true that they can be damaged if you run them in air. I didn't want to argue, but its true that you can damage "projectors" if you drive them in air, and the OP is using it as a projector by your definition.

    Sorry if it seemed to bug you that I said you can damage it by driving it in the air.
     
  12. Jan 26, 2012 #11

    Bobbywhy

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    DragonPetter, Thank you for your thoughtful comments about hydrophones and projectors. No, it didn't bug me one bit, thank you. I too have had Urick's books (first and second editions) on my bookshelf since 1982. Every sonar engineer I have ever known would consider Urick's book the "bible" of sonar.

    As for our discussion: Since we seem to agree on definitions, the purpose of Physics Forums seems to be validated.

    I feel confident that we would also agree that a hydrophone is analagous to a microphone. One is used in the water, the other in air. Is there any reason anyone would apply a high power drive signal to a microphone? That would surely damage/destroy it. Same applies to a hydrophone.

    Peace, Bobbywhy
     
  13. Jan 30, 2012 #12
    Wow, you have had that book since before I was born. I agree with everything you said, and since the OP is using his hydrophone in the microphone mode, I only thought I should caution him that it can be damaged when used that way in air, even though it probably won't with the power he said he's driving it with.

    Do you work or do research in sonar? I got into the field 2 years ago and am already back out of it.
     
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